The invention relates to an impulse suppression apparatus and a related method, and more particularly, to an impulse suppression apparatus and a related method utilizing a decision-aided reconstruction procedure.
Generally, the radio frequency communication systems suffer more interferences, such as atmospheric interference and jamming, than the wired transmission communication systems. Some interferences appear as Gaussian model, and some interferences generated by electrical self-starters, power lines, or high-current switches, are called impulse noises. Since the impulse, the short for impulse noise, contains a lot of power in a short time interval, the influence of the impulse on a received signal is greater than other kinds of noise on the received signal. As a result, it is an important issue to receivers to detect and suppress the impulse noises.
Take the radio frequency communication systems for transmitting audio and video data as an example, such as a Digital Video Broadcasting-Terrestrial (DVB-T) system. Since the impulse contains high power, the audio-output equipments suffering the impulse may generate a popping noise, and the image output equipment suffering the impulse may show a distorted image on its screen. It goes without saying that the popping noise and distorted image make the end users feel uncomfortable. Therefore, when designing the DVB-T system, the system designer would rather sacrifice some signal quality to suppress the impulse than hope the end users being tolerant on the popping noise and the distorted image. A common method for suppressing impulse noise is comparing the absolute value of the receive signal with a threshold value. If the absolute value of the receive signal is greater than the threshold value at a time point, the system determines the received signal is influenced by an impulse at the time point and sets the value of the received signal at the time point to be zero. Please refer to FIG. 1. FIG. 1 is a schematic diagram of the operation of a related art impulse suppressing method. As shown in FIG. 1, the input signal is a digital signal, and corresponds to different values at different sampling time, where the absolute value of the input signal represents the magnitude of the input signal at a sampling time. The solid line denotes the actual magnitude of the input signal, and the dotted line represents the magnitude of an impulse noise. At the sampling time tb, the magnitude of the input signal is “3”, and the input signal suffers the impulse noise, whose magnitude is “6”. Therefore the detected magnitude of the input signal at the sampling time tb is “9”. If the threshold value mentioned above is “8”, the receiver determines the input signal is influenced by an impulse noise at sampling time tb, and sets the value of output signal at the sampling time tb to be “0”. In the same manner, the receiver also sets the values of the output signal at the sampling time ta, tc, td to be zero. Although the impulse noises at the sampling time ta, tb, tc, td are suppressed, the actual value of the input signal at the sampling time ta, tb, tc, td are suppressed too. For example, at the sampling time tb, the magnitude of the impulse noise is “6”, and the actual magnitude of the input signal is “3”. As the value of the output signal is set to be zero, both of the magnitude of the impulse noise and the magnitude of the input signal are suppressed. As a result, the procedure mentioned above distorts the data transmitted via the input signal.
In some application, the users will not be aware the distortion because of the limitation of human sense organs. For example, regarding the image transmission system, the audience will not be aware the difference of a pixel. Hence, if the input signal is distorted at a few sampling times the audience will not be aware. This phenomenon also happens in audio data transmission system. However, as the quality of the audio and video equipments raise, required quality of image and sound increases. In summary, although the related art method can suppress the impulse noise obviously, the quality of the received signal is reduced accordingly. As a result, the related art method cannot present the transmitted audio and video data correctly.